This invention relates to a lamp comprising a halogen inner lamp that is attached to a stem in the lamp.
Ordinary household lamps with an incandescent filament have been known for a long time. These lamps comprise a filament enclosed in a glass envelope or jacket. These lamps, while relatively cheap and reliable, are not energy-efficient. Compact fluorescent lamps have a higher efficiency, but they are more expensive, while many people perceive their spectrum as less natural. Therefore, it has been proposed to incorporate into a traditional glass bulb a smaller halogen light source, in the form of an inner lamp, having its own envelope and filament. Such inner lamps can be more efficient, because it is easier to maintain the ideal conditions for the heating of a filament within a small volume, surrounded by a relatively thick, and therefore strong envelope. Since it is a major objective to produce these lamps in a cost-effective manner, it is sought to use standard and proven lamp-manufacturing technology to the maximum possible extent. For this reason, the incorporation of the inner lamp into the larger glass envelope may be realized by attaching the inner lamp to a glass stem within the outer envelope. This glass stem traditionally serves multiple functions. Firstly, it includes the sealed leads that normally supply the electric current to the filament in the lamp. Secondly, the glass stem also contains the exhaust tube, through which the outer envelope is finally evacuated. Since these functions are also needed for a lamp with an inner lamp, it is desirable to maintain this functional element.
For example, U.S. Pat. No. 6,262,534 discloses a lamp with an external glass envelope and containing an inner lamp as a light source. There is also a protective shroud surrounding the inner lamp. The inner lamp and the shroud is connected to leads in a glass stem. The light source in U.S. Pat. No. 6,262,534 is a relatively short tungsten halogen incancdescent lamp having two outer leads exiting the lamp through a pinch. The leads are parallel to each other, and thereby define the plane of the pinch. The outer leads are sealed directly to the glass stem. Therefore, the main plane of the stem—as defined by the parallel leads within the stem—is parallel with the main plain of the pinch. However, this arrangement is only applicable with single-ended halogen inner lamps. Double-ended lamps are easier to manufacture, hence they are more preferred.
Another type of commercially available household lamp comprises an outer bulb enclosing an inner halogen lamp, supported by two leads in a glass stem. The inner halogen lamp is a double-ended lamp with two pinched ends. The inner lamp is attached to one of the leads with the help of a clamp, which is welded to one of the leads. The clamp is an essentially C-shaped and folded metal device, which clamps onto an edge of the pinch at one end of the C, and welded to the lead at the other end of the C. In this manner, the weight of the inner lamp is supported largely by the clamp. The disadvantage of this inner lamp-stem assembly is the relatively complicated shape of the clamp, and the fact that the pinch is relatively far from the stem.
International Patent Application No. WO 02/33731 discloses a lamp having a stem and an inner lamp connected to the stem. The inner lamp is a straight double-ended halogen lamp, with a straight filament and two leads which extend from a tubular inner lamp jacket at its two ends. The two ends are therefore sealed with a pinch in a known manner, sealing a connecting foil in the pinch. There is a pinch on both ends of the inner lamp. The leads of the halogen inner lamp are welded to external leads, and these latter are embedded in the stem of the lamp.
This latter arrangement has the advantage that a relatively cheap, mass-produced halogen light source may be incorporated into a standard light bulb, using largely the same manufacturing equipment which is used for manufacturing more traditional incandescent bulbs. Notably, the manufacturing equipment for producing the stem with leads, and the subsequent mounting of the external envelope to the stem may remain the same. The only difference is the light source itself, i.e. the use of an inner lamp (also termed as inner burner) instead of a free-standing filament. Though in some applications it would be desirable to have shorter double-ended inner lamps, it contradicts with certain other criteria. Firstly, in order to be able to generate a suitable light output, such a double-ended halogen lamp must have a filament reaching a certain length, but the length of the filament is limited by the length of the lamp, due to a number of technical considerations. Generally, the longer the filament, the higher the achievable light output. Secondly, there is also a practical lower limit to the size of double-ended inner lamps with pinched ends. Since the two pinches take up approx. 10-15 milimeters from both ends, the effective length of the filament is approx. half of that of the whole bulb. Therefore, double-ended inner lamps usually have a length above 50-55 milimeters, which is difficult to reduce further. For example, a 10% shorter bulb will mean a 20% decrease in the effective filament length, due to the more or less fixed length of the pinches. However, the incorporation of a longer straight inner lamp into the lamp may cause problems. Specifically, it may be problematic to incorporate a double-ended halogen lamp into a smaller lamp, such as a standard B-35 candle lamp.
Therefore, there is a need for relatively small lamps which incorporate a relatively long inner lamp, while keeping the small form factor of the lamp. Also, there is a need for a lamp which may be sold as a standard household lamp, which is easy to manufacture and which, at the same time, incorporates a halogen inner lamp. There is also need for an improved inner lamp—stem configuration which support the above goals. It is sought to provide a household lamp, which has a relatively simple structure, and which does not require any radical change in exisiting manufacturing facilities.